Depends on how frequently you'll hunt elk. If I were to pick a cartridge for shooting an elk at 700 yards I wouldn't go any smaller than a 300 Win Mag. That would be my recommendation for a good all-around rifle. Shoot 200 grain Accubonds, 208 ELD Match, 212 ELD-X, or 215 Berger Hybrids. If you're hunting mostly deer at longer ranges, and only hunt elk on occasion, a fast 7mm would be a great choice. I think they're decent elk guns out to 500 yards or so but I still prefer a .30 or .338 for elk. If you choose a 7mm take a look at the 7mm-300 Win Mag. It will do pretty well with the 180 grain bullets.